(1) Field of the Invention
The present invention relates to a multilayer optical disc having multiple recording layers and an optical disc drive that can easily identify the layers of the multilayer optical disc.
(2) Description of the Related Art
In recent years, BD (Blu-ray) optical discs have been developed with an increased number of recording layers to obtain larger recording capacities. Two-layer discs have been already put into practical use. Optical discs, each having three or at least four recording layers (hereinafter, will be referred to as multilayer discs), are expected to be standardized in the future to achieve further increases in capacity.
On a multilayer optical disc, a light spot has to be moved to a target recording layer (target layer) to perform focus servo control before recording/reproduction. In order to identify whether the light spot has been moved to the target layer or not, generally, address information is extracted from a reproduced signal or a wobble signal from the optical disc and is decoded to identify whether the current recording layer is the target layer or not.
In addition to a method using address information, for example, International Publication No. WO 00/23990 discloses an optical information recording medium having a management region for recording identification information about deviations in the circumferential direction between sector address portions, the management region being provided in at least one of the information layers (recording layers) of the medium. The identification information is provided in various forms or at different radial positions between the information layers to recognize the identifiers of the information layers, and an identifier pattern may include the sector address portions, a bit string used in the management region, or guide grooves formed in specific conditions in data portions.